Method of providing data, voice, and SMS services to LTE subscribers roaming in 2G/3G visited networks

ABSTRACT

A method of providing voice call, data, and SMS services to a user equipment roaming in a 2G/3G visited network and subscribed to an LTE home network. An Interworking Function communicates with both the visited network and the home network. The Interworking Function translates between Mobile Application Part (MAP) protocol used by the 2G/3G visited network and Session Initiation Protocol (SIP) used by the LTE home network. The Interworking Function establishes both a MAP Registration with the 2G/3G visited network and also a SIP Registration with the LTE home network, thereby enabling provision of voice call, data, and SMS services to the roaming UE.

PRIORITY CLAIM

This application is a continuation of and claims priority to U.S.Nonprovisional patent application Ser. No. 15/695,620 filed Sep. 5,2017, entitled “METHOD OF PROVIDING DATA, VOICE, AND SMS SERVICES TO LTESUBSCRIBERS ROAMING IN 2G/3G VISITED NETWORKS.”

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to mobile communications. More specifically, theinvention pertains to a method of providing voice call, data, and SMSroaming services to VoLTE/LTE subscribers visiting 2G/3G networks.

2. Brief Description of the Related Art

International travel has become ubiquitous and those engaging in suchtravel create a strong demand for data roaming services when outside oftheir home mobile network coverage area. In the United States and theEuropean Union, a large percentage of mobile networks are Long TermEvolution (LTE) networks. In many other markets, however, data, voice,and short message services (SMS) are provided predominantly orexclusively via 2G/3G networks. Because many LTE home networks lack core2G/3G network components, these LTE networks are unable to provideout-bound roaming services to their subscribers when they are roamingwithin 2G/3G serve networks. Currently, to provide coverage for an LTEsubscriber in 2G/3G market, the LTE home network operators would have toexpend substantial resources to acquire and integrate 2G/3G core networkcomponents into their network.

Although LTE coverage is rapidly expanding, the roaming traffic is notexpanding at the same pace and in many geographic locations only 2G/3Gmobile networks are available while roaming. Lack of ubiquitous LTEcoverage presents a challenge for LTE-only mobile networkoperators—commonly referred to as Greenfield operators—which do not have2G/3G network components and do not have circuit switch fall backcapabilities, because they are unable to provide seamless roamingexperience to their subscribers. To have a capability to providecoverage in a 2G/3G market, Greenfield operators would have to expendsignificant resources to deploy 2G/3G core network elements within theirnetworks.

Lack of 2G/3G network components presents a two-fold problem for LTEnetwork operators: on one hand, the LTE network operators are unable toprovide in-bound voice and SMS roaming services to 2G/3G subscribers; onthe other hand, the LTE network operators are also unable to provideout-bound roaming services to their own subscribers who are visiting2G/3G networks. U.S. patent application Ser. No. 14/230,633, which iscurrently assigned to SYNIVERSE® and will soon issue into a patent,discloses and claims a method that addresses the first problem listedabove by enabling the LTE networks to provide in-bound roaming to 2G/3Gsubscribers. However, until the present invention, an efficient andeffective solution to the problem of enabling the LTE network to provideout-bound roaming services to a subscriber visiting a 2G/3G network wasnot known in the art.

SUMMARY OF THE INVENTION

The present invention enables an LTE-only (Greenfield) mobile networkoperator or a Greenfield operator to provide out-bound roaming servicesto their subscribers in 2G/3G markets without deploying 2G/3G corenetwork elements at their home networks. The present invention is amethod of providing voice call, short message service (SMS), and dataroaming services to a User Equipment (UE) subscribed to an LTE homepublic mobile network (HPMN) while the UE is roaming in a 2G/3G visitedpublic mobile network (VPMN). The invention involves an InterworkingFunction (IWF) having a Proxy Call Session Control Function (P-CSCF), aHome Location Register (HLR) and a Short Message Service Center (SMSC)components. The IWF is in communication with both the HPMN and the VPMN.

When the VPMN receives a request from the UE to access voice call, SMS,and/or data roaming services in the VPMN, the VPMN initiates anauthentication procedure. To authenticate the UE in the VPMN, the IWFconverts between a Mobile Application Part (MAP) protocol of the VPMNand a Diameter protocol of the HPMN.

After the UE is authenticated into the VPMN, the IWF receives a MAPLocation Update (LU) Message from the VPMN. The IWF converts the MAP LUMessage into a Diameter S6d interface Update Location Request (ULR)Message and sends the ULR Message to a Home Subscriber Server (HSS) ofthe HPMN. The HSS returns a S6d Profile for the UE, wherein the S6dprofile is a Packet Switched (PS) Profile. Instead of sending the PSProfile returned by the HSS, the IWF sends to the VPMN a pre-definedCircuit Switch (CS) Profile. Responsive to the VPMN accepting the CSProfile, the IWF establishes a CS Registration with the VPMN.

The IWF also initiates a SIP Registration in the HPMN by sending a SIPRegister message to the HSS. Responsive to receiving a SIP Response fromthe HPMN, the IWF establishes a SIP Registration with the HPMN. Becausethe IWF concurrently maintains the CS Registration with the VPMN and theSIP Registration with the HPMN, the IWF enables provision of the voicecall, SMS, and data roaming services to the UE subscribed to the HPMNwhile the UE is roaming in the VPMN, wherein HPMN is an LTE mobilenetwork and the VPMN is a 2G/3G mobile network.

In an embodiment, to authenticate the UE in the VPMN, the IWF converts aMAP Send Authentication Information (SAI) Message originating from theVPMN to a Diameter S6d interface Authentication Information Request(AIR) Message and transmits the AIR Message to the HSS of the HPMN. TheIWF converts an Authentication Information Answer (AIA) Message receivedfrom the HSS to a MAP SAI Response Message and sends the MAP SAIResponse Message to the VPMN.

In an embodiment, the IWF is hosted on the IP Packet eXchange (IPX)network.

In an embodiment, to register the UE for data services in the VPMN aServing General Packet Radio Service (GPRS) Support Node (SGSN) of theVPMN sends a GPRS Location Update message to the IWF, and the IWFreturning the PS profile to the SGSN.

In an embodiment, delivery of voice calls from a Calling Party to the UEinvolves the following steps. A Serving Call Session Control Function(S-CSCF) of the HPMN forwards a SIP Invite message to the P-CSCFcomponent of the IWF. The HLR component of the IWF queries a VisitedLocation Register (VLR) of the VPMN for a Mobile Subscriber RoamingNumber (MSRN) assigned to the UE and returns the MSRN to the P-CSCFcomponent of the IWF. The P-CSCF component of the IWF the sends the SIPInvite message to Media Gateway (MG) of the HPMN. For IMS originatingcalls—i.e., the Calling Party is subscribed to an IMS network—the MGprovides interworking between Integrated Services Digital Network UserPart (ISUP) and SIP signaling for call control.

In an embodiment, call delivery for calls originating from the UE to aCalled Party that is an IMS subscriber involves the following steps. AMobile Switching Center (MSC) of the VPMN sends an ISUP message to a MGof the HPMN. The MG then sends a SIP Invite to a S-CSCF of the HPMN. TheS-CSCF routes the SIP Invite to a P-CSCF within the IMS subscriber'shome network.

For calls originating from the UE to a Called Party subscribed to aPublic Switched Telephone Network (PSTN), the MSC of the VPMN sends anISUP message to a GMSC of the subscriber's home network. The GMSCrequests a MSRN assigned to the Called Party from a HLR within theCalled Party's network. The GSMC uses the MSRN to route the call to theCalled Party.

To send an SMS message originating from the UE, a MSC of the VPMN routesthe SMS message to the IWF. The IWF retrieves the UE's Mobile StationInternational Subscriber Directory Number (MSISDN) from the SMS message.The P-CSCF component of the IWF sends a SIP SMS Message to a S-CSCF ofthe HPMN. The S-CSCF then forwards the SIP SMS Message to an IP-SMSCwithin the HPMN. The SMS Service Center (SC) address provisioned in theUE is that of the IWF.

The following are several exemplary advantages achieved by the inventionover the prior art methods. First, because 2G/3G networks are moreprevalent than LTE networks, there are more potential 2G/3G roamingpartners then there are LTE roaming partners. The present inventionenables an LTE subscriber to have seamless service while roaming in the2G/3G networks. Greenfield operators can use 2G/3G sponsored networksfor greater coverage. The present invention eliminates gaps in coveragewhere LTE is not available.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference should be made tothe following detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 is diagram schematically depicting architecture of the presentinvention;

FIG. 2 is a signaling call flow of a procedure for authenticating a UEin the 2G/3G visited network;

FIG. 3 is a signaling call flow of a procedure for registration of theUE in the 2G/3G visited network and LTE home network;

FIG. 4 is a flowchart illustrating the steps of establishing a CSRegistration with VPMN and a SIP Registration with HPMN;

FIG. 5 is a signaling call flow of a procedure for data registration ofthe UE in the 2G/3G visited network and LTE home network;

FIG. 6 is a signaling call flow of a procedure for delivery of a voicecall originating from a Calling Party subscribed to an IMS network tothe UE;

FIG. 7 is a signaling call flow of a procedure for delivery of a voicecall originating from a Calling Party on a PSTN network to the UE;

FIG. 8 is a signaling call flow of a procedure for origination of avoice call from the UE to a Called Party subscribed to an IMS network;

FIG. 9 is a signaling call flow of a procedure for origination of avoice call from the UE to a Called Party on a PSTN network;

FIG. 10 is a signaling call flow of a procedure for sending an SMSmessage from the UE from to an intended recipient;

FIG. 11 is a signaling call flow of a procedure for sending an SMSmessage from a third party to the UE;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention pertains to network communications. More specifically, theinvention is a method of enabling data, voice, and SMS services to anLTE home network subscriber roaming in a 2G/3G serve network. Thegeneral architecture of the invention is depicted in FIG. 1. A userequipment (UE) 12 is subscribed to an LTE Home Mobile Network (HPMN) 14and is roaming in a 2G/3G Visited Mobile Network (VPMN) 16. HPMN 14includes the following network components: Packet Data Network Gateway(P-GW)/Gateway GPRS Support Node (GGSN) 18, Home Subscriber Server (HSS)20, IP-SMCS 22, IP-SM-GW 24, Interrogating Call State Control Function(I-CSCF) 26, Serving Call State Control Function (S-CSCF) 28, (MediaGateway) MG 30, and Application Server (AS) 32. VPMN 16 includes thefollowing network components: Serving GPRS Support Node (SGSN) 34,Mobile Switching Center (MSC) 36, and Visitor Location Register (VLR)38.

The invention introduces an Interworking Function (IWF) 40 hosted by anInternetwork Packet Exchange (IPX) network 42. IWF 40 includes a ShortMessage Service Center (SMSC) 43, a Proxy Call Session Control Function(P-CSCF) 44, and Home Location Register (HLR) 45. IPX network 42 alsohosts a Diameter Proxy 46. Diameter Proxy 46 communicates with IWF 40via Diameter Protocol. Diameter Proxy also communicates with HSS 20 ofHPMN 14 via Diameter Protocol.

With respect to HPMN 14, IWF 40 establishes a Mobile Application Part(MAP) connection with IP-SM-GW 24 and a SIP connection with I-CSCF 26.With respect to VPMN 16, IWF 40 establishes a MAP connection with VLR38. IWF 40 communicates with an Authentication Server 48 using MAPsignaling.

IPX network 42 also hosts Diameter Proxy 46, which communicates with HSS20 of HPMN 14 and with IWF 40 via Diameter protocol. PGW/GGSN 18 of HPMN14 establishes a GTP Tunnel with SGSN 34 of VPMN 16 for transmission ofdata.

Authentication and Service Registration

FIG. 2 is a signaling diagram depicting the process of authenticating UE12 onto VPMN 16. UE 12 must have a GSM radio compatible with 2G/3Gservices. In step 102, UE 12 sends an Attach Request to MSC 36/VLR 38.In step 104, VLR 38 sends a Send Authorization Information (SAI) messagevia MAP protocol to IWF 40. IWF 40 converts the MAP: SAI message to aDiameter S6d interface Authorization Information Request (AIR) messageand, in step 106, sends the converted message to HSS 20 of HPMN 14 torequest 2G/3G authorization vectors. In step 108, HSS 20 returns the2G/3G authorization vectors in a Diameter S6d Authorization InformationMessage (AIA) Response message to IWF 40. In step 110, IWF 40 convertsthe AIA Response message into a MAP SAI Acknowledgement message andsends the converted message to VLR 38 of VPMN 16. At this pointauthentication is completed.

Once the authentication into VPMN 16 has been completed, theregistration procedure commences. The registration procedure isschematically depicted in FIG. 3. In step 112, VLR 38 sends a MAPLocation Update (LU) message to IWF 40 to be routed to HPMN 14. IWF 40converts the MAP:LU message into a Diameter S6d interface UpdateLocation Request (ULR) message and, in step 114, sends the convertedmessage to HSS 20 of HPMN 14. In step 116, HSS 20 responds to IWF 40with a Diameter S6d Update Location Answer (ULA) message.

IWF 40 does not forward the S6d profile for UE 12 received in the S6dULA message to VPMN 16 because the received S6d profile is a PacketSwitched (PS) profile incompatible with 2G/3G network's VLR 38. Instead,IWF 40 retrieves a pre-defined 2G/3G Circuit Switched (CS) profile and,in step 118, sends the CS profile to VLR 38 in a MAP Insert SubscriberData (ISD) message. After the CS profile for UE 12 is accepted by VLR 38of VPMN 16, VLR 38 returns a MAP ISD Acknowledgement message to IWF 40in step 120.

IWF 40 also establishes a SIP Registration with HPMN 14. In step 122,P-CSCF 44 in IWF 40 initiates a VoLTE Registration to the IMS Core ofHPMN 14 by sending a SIP Register message to S-CSCF 28. There is aninternal interface between P-CSCF 44 and HLR 45 components of IWF 40. Instep 124, S-CSCF 28 sends a Diameter Cx/Dx Server-Assignment-Request(SAR) message to HSS 20. In step 126, HSS 20 responds to S-CSCF 28 witha Diameter Cx/Dx Server Assignment Answer (SAA) message. In step 128,S-CSCF 28 sends a SIP 200 OK message to IWF 40. On completion ofRegistration, S-CSCF 28 updates the current IMS server address into HSS20 and also completes any third-party Registrations to TAS and otherApplication Servers (AS) in accordance with the local policy.

FIG. 4 is a flow chart illustrating the registration procedure. In step202, VPMN 16 receives a request from UE 12 to access voice call, SMS,and/or data roaming services. In step 202, UE 12 is authenticated inVPMN 16, wherein IWF 40 converts between a MAP protocol of the VPMN 16and a Diameter protocol of HPMN 14 during the authentication step. Instep 204, the IWF receives a MAP LU Message from VPMN 16. In step 206,IWF 40 converts the MAP LU Message into a Diameter S6d interface ULRMessage and, in step 208, sends the ULR Message to HSS 20 of HPMN 14. Instep 210, HSS 20 returns a S6d Profile for the UE, the S6d profile beinga Packet Switched (PS) Profile. In step 212, IWF 40 sends to VPMN 16 apre-defined Circuit Switch (CS) Profile instead of the PS Profilereturned by HSS 20. In step 214, responsive to VPMN 16 accepting the CSProfile, IWF 40 establishes a CS Registration with VPMN 16. IWF 40 alsoinitiates SIP Registration in HPMN 14. In step 216, responsive toreceiving a SIP Response from HPMN 14, IWF 40 establishes SIPRegistration with HPMN 14. IWF 40 maintains the CS Registration withVPMN 16 and SIP Registration with HPMN 14, which enables provision ofthe voice call, SMS, and data roaming services to UE 12.

Data Registration

FIG. 5 illustrates the process of registering for data services inaccordance with the invention. In step 128, SGSN 34 sends MAP GeneralPacket Radio Service (GPRS) LU message to IWF 40 to be routed to HPMN14. IWF 40 converts the MAP:GPRS-LU message into a Diameter S6dinterface ULR message and, in step 130, sends the converted message toHSS 20 of HPMN 14. In step 132, HSS 20 responds with a Diameter S6d ULAmessage. In step 134, IWF 40 returns a 2G/3G PS profile to SGSN 34 ofVPMN 16 in a MAP:ISD transaction. Once the 2G/3G PS Profile has beenaccepted by SGSN 34, SGSN 34 sends a MAP:ISD Ack message to IWF 40 instep 136. Finally, IWF 40 responds to SGSN 34 with a MAP:GPRS UL Ackmessage in step 138, which completes registration for roaming dataservice for UE 12.

Call Delivery—IMS Origination

The procedure for call delivery for phone call originating from an IMSsubscriber is depicted in FIG. 6. Any incoming calls for UE 12 willoriginate as SIP-Invite messages in which UE 12 Mobile StationInternational Subscriber Directory Number (MSISDN) is represented as aSIP Uniform Resource Identifier (URI). As shown in step 140, because UE12 is IMS registered in HPMN 14, the SIP-Invite message is directed toS-CSCF 28 in HPMN 14, in which UE 12 is registered. In step 142, S-CSCF28 forwards the SIP-Invite message for the incoming call to P-CSCF 44component of IWF 40 via which UE 12 is registered. In step 144, HLR 45of IWF 40 sends a MAP Provide-Roaming-Number (PRN) message to VLR 38 ofVPMN 16 where UE 12 is attached. In step 146, VLR 38 returns a MobileSubscriber Roaming Number (MSRN) assigned to UE 12 by VPMN 16. VLR 38sends the MSRN in MAP:PRN-Response message to HLR 45 within IWF 40. HLR45 returns the MSRN to P-CSCF 44 within IWF 40. In step 148, P-CSCF 44sends a SIP-Invite message to MG 30 within HPMN 14 using the MSRN as aRequest-URI in the SIP-Invite. MG 30 converts the SIP-Invite message toan Integrated Services Digital Network User Part (ISUP) Initial AddressMessage (IAM) and sends it to MSC 36 within VPMN 16 in step 150. Becausethe incoming call is from IMS subscriber and uses SIP signaling, MG 30provides interworking between ISUP and SIP signaling to enable callcontrol and interworking between Time Division Multiplexing (TDM) andReal-time Transport Protocol (RTP) for media.

Call Delivery—PSTN Origination

FIG. 7 schematically illustrates the procedure for call delivery forcalls incoming from a Public Switched Telephone Network (PSTN). Eachsuch incoming call originates as ISUP:IAM, which is received by MG 30 ofHPMN 14 in step 152. In step 154, because UE 12 is IMS-registered inHPMN 14, MG 30 directs the incoming call to S-CSCF 28 by sendingSIP-Invite message to S-CSCF 28. In the SIP-Invite, MSISDN of UE 12 isrepresented as a SIP URI. In step 156, S-CSCF 28 forwards the SIP-Invitemessage for the incoming call to P-CSCF 44 of IWF 40. In step 158, HLR45 of IWF 40 send a GSM PRN MAP message to VLR 38 of VPMN 16 where UE 12is attached. VLR 38 returns MSRN of UE 12 to HLR 45 of IWF 40 in MAPPRN-Response. HLR 45 returns the MSRN to P-CSCF 44 of IWF 40. In step162, P-CSCF 44 sends a SIP-Invite to MG 30 within HPMN 14 using the MSRNas the Request-URI in the SIP-Invite. MG 30 converts the SIP Invite intoan ISUP IAM and sends it to MSC 36 of VPMN 16 in step 164. In the caseof PSTN originating call, MG 30 does not need to provide SIP/RTP toISUP/TDM inter-working because both call-legs are connected usingISUP/TDM.

Outgoing Call—IMS Termination

FIG. 8 schematically depicts the process for establishing an outgoingcall from UE 12 to a device in an IMS domain. Each outgoing call made byUE 12 originates as ISUP:IAM, which is sent from MSC 30 of VPMN 16 inwhich UE 12 is attached to MG 30 of HPMN 14 as shown in step 166. Instep 168, MG 30 forwards the call as a SIP-Invite to S-CSCF 28 of HPMN14 in which UE 12 is registered. The SIP Invite represents MSISDN of thecall recipient as SIP URI. In step 170, S-CSCF 28 routes the SIP Inviteto P-CSCF 50 of the Called-Party. MG 30 provides interworking betweenISUP and SIP for call control and between TDM and RTP for media in theIMS domain.

Outgoing Call—PSTN Termination

FIG. 9 schematically depicts the process for establishing an outgoingcall from UE 12 to a Called Party on a PSTN. This process is similar toregular GSM roaming. Each outgoing call made by UE 12 originates asISUP:IAM, which, in step 172, is sent from MSC 30 of VPMN 16, in whichUE 12 is attached, to GMSC 52 of Called-Party's HPMN 54. In step 174,GMSC 52 requests MSRN of the Called-Party from HLR 56 within HPMN 54 viaa MAP Send Routing Information (SRI) message. In step 176, HLR 56requests the MSRN from MSC 58 where the Called-Party is currentlyattached using a MAP:PRN message. In step 178, MSC 58 returns therequested MSRN via a MAP:PRN-Response message to HRL 54. In step 180,HLR 56 sends a MAP: SRI-Response message to GMSC 52. In step 182 GMSC 52uses the MSRN to route the call the Called-Party by sending ISUP IAMmessage to MSC 58 of HPMN 54 in which the Called-Party is registered.HPMN 14 to which UE 12 is subscribed is not involved in originatingcalls made to the PSTN while the user is roaming in a VPMN 16.

SMS Mobile-Originating

FIG. 10 illustrates the process for sending an SMS message originatingfrom UE 12. The SMSC address provisioned in UE 12 is the address of SMSC43 within IWF 40. Thus, when UE 12 sends an SMS message, MSC 36 of VPMN16 uses Global Title (GT) routing to route the message to SMSC 43 of IWF40 as MAP Forwarded SM-MO message in step 184. IWF 40 retrieves UE 12'sMSISDN from the SMS payload. In step 186, P-CSCF 44 of IWF 40 sends aSIP SMS Message with the SMS MO TPDU towards S-CSCF 28 of HPMN 14 inwhich UE 12 is registered. In step 188, S-CSCF 28 forwards the SIP SMSMessage to IP-SMSC 22 of HPMN 14. In step 190, IP-SMSC 22 responds toS-CSCF 28 with SIP 200 OK message. In step 192, S-CSCF 28 forwards SIP200 OK message to IWF 40. In step 194, SMSC 43 of IWF 40 sends MAPForwarded SM-MO Ack message to MSC 36 of VPMN 16.

SMS Mobile-Terminating

FIG. 11 illustrates how UE 12 receives SMS messages. When a SendingParty sends an SMS to UE 12, IP-SMSC 22 of HPMN 14 sends a SIP SMSMessage with SMS MT TPDU to S-CSCF 28 in step 196. In step 198, S-CSCF28 forwards this SIP SMS Message to P-CSCF 44 of IWF 40. IWF 40retrieves the SMS MT TPDU from the SIP SMS Message and identifiesterminating MSISDN. IWF 40 retrieves the address MSC 36 using SRI-SM toHLR. In step 200, SMSC 43 of IWF 40 GT routes a MAP Forwarded SM-MTmessage to MSC 36 of VPMN 16 in which UE 12 is attached. MSC 36 respondswith a MAP Forwarded SM-MT message to SMSC 43 of IWF 40 in step 202.P-CSCF 44 of IWF 40 sends SIP 200 OK message to S-CSCF 28 in step 204.In step 206, S-CSCF 28 forwards the SIP 200 OK message to IP-SMSC 22.

Hardware and Software Infrastructure Examples

The present invention may be embodied on various platforms. Thefollowing provides an antecedent basis for the information technologythat may be utilized to enable the invention.

Embodiments of the present invention may be implemented in hardware,firmware, software, or any combination thereof. Embodiments of thepresent invention may also be implemented as instructions stored on amachine-readable medium, which may be read and executed by one or moreprocessors. A machine-readable medium may include any mechanism forstoring or transmitting information in a form readable by a machine(e.g., a computing device). For example, a machine-readable medium mayinclude read only memory (ROM); random access memory (RAM); magneticdisk storage media; optical storage media; flash memory devices;electrical, optical, acoustical or other forms of propagated signals(e.g., carrier waves, infrared signals, digital signals, etc.), andothers. Further, firmware, software, routines, instructions may bedescribed herein as performing certain actions. However, it should beappreciated that such descriptions are merely for convenience and thatsuch actions in fact result from computing devices, processors,controllers, or other devices executing the firmware, software,routines, instructions, etc.

The machine-readable medium may be, for example, but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device, or any suitable combinationof the foregoing. More specific examples (a non-exhaustive list) of thecomputer readable storage medium would include the following: anelectrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flashmemory), an optical fiber, a portable compact disc read-only memory(CD-ROM), an optical storage device, a magnetic storage device, or anysuitable combination of the foregoing. In the context of this document,a computer readable storage medium may be any non-transitory, tangiblemedium that can contain, or store a program for use by or in connectionwith an instruction execution system, apparatus, or device.

A machine-readable signal medium may include a propagated data signalwith machine-readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Amachine-readable signal medium may be any machine-readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device. However, asindicated above, due to circuit statutory subject matter restrictions,claims to this invention as a software product are those embodied in anon-transitory software medium such as a computer hard drive, flash-RAM,optical disk or the like.

Program code embodied on a machine-readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wire-line, optical fiber cable, radio frequency, etc., or any suitablecombination of the foregoing. Machine-readable program code for carryingout operations for aspects of the present invention may be written inany combination of one or more programming languages, including anobject oriented programming language such as Java, C#, C++, Visual Basicor the like and conventional procedural programming languages, such asthe “C” programming language or similar programming languages.

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bymachine-readable program instructions.

Glossary of Claim Terms

General Packet Radio Service (GPRS) is a packet oriented mobile dataservice on the 2G and 3G mobile communication system's global system formobile communications (GSM).

Home Location Register (HLR) is the main database of permanentsubscriber information for a mobile network and contains pertinent userinformation, including address, account status, and preferences.

Home Public Mobile Network (HPMN) is a network to which a roaming UE hasa subscription.

Home Subscriber Server (HSS) is a server that can store and processsubscription data and other information about each subscriber authorizedto use the network.

IMS Core is the central network component of a communication system thatis based on IP multimedia service protocols. The core network primarilyprovides interconnection and transfer between edge networks.

Interworking Function (IWF) a custom function configured to translatebetween MAP and Diameter protocols to enable interoperability of 2G/3Gserve networks and LTE home networks.

International Mobile Subscriber Identity (IMSI) is a number assigned bya mobile system operator to uniquely identify a UE.

IP Multimedia Subsystem (IMS) is service based architecture that usesInternet protocol (IP) based systems to provide enhanced multimediaservices. IMS evolved from the evolution of the 3rd generation mobiletelephone standards that enabled users to access multimedia servicesusing any type of access network that could use Internet protocols.

IP Packet eXchange (IPX) is a network used to exchange IP-based traffic.IPX interconnects multiple mobile networks through the use of commontechnical specifications based on IP.

Mobile Switching Center (MSC) is a 2G/3G network component that handlesconnections between mobile users within the network and is responsiblefor routing voice calls and SMS text messages.

Mobile Subscriber Roaming Number (MSRN) is a temporarily telephonenumber assigned to a UE which roams into the VPMN.

Mobile Station International Subscriber Directory Number (MSISDN) is anumber used to identify a mobile phone number internationally.

Proxy Call Session Control Function (P-CSCF) is an entry point to theIMS domain and serves as the outbound proxy server for the UE. The UEattaches to the P-CSCF prior to performing IMS registrations andinitiating SIP sessions.

Public Switched Telephone Network (PSTN) is the aggregate of the world'scircuit-switched telephone networks that are operated by national,regional, or local telephony operators, providing infrastructure andservices for public telecommunication.

Serving Call Session Control Function (S-CSCF) a SIP server located inthe HPMN. S-CSCF uses the Diameter Cx interface to the HSS to downloaduser profiles and upload user-to-S-CSCF associations.

Session Initiation Protocol (SIP)-Register message is a message sentfrom a UE used to register with a network.

Session Initiation Protocol (SIP)-Invite message is a message sent froma UE/calling party used to initiate a phone call with a called party.

Short Message Service Center (SMSC) is a network element in the mobiletelephone network and is configured to store, forward, convert anddeliver Short Message Service (SMS) messages.

User Equipment (UE) is a device that can connect to a communicationsystem. Examples of UE devices include multimedia mobile telephones,personal computers, transceivers that are installed in vehicles or fixedwireless units.

Visitor Location Register (VLR) is a database in a mobile communicationsnetwork associated to a Mobile Switching Center (MSC). The VLR containsthe locations of mobile subscribers present in the service area of theMSC.

Visited Public Mobile Network (VPMN) is a mobile network used by amobile subscriber while roaming.

The advantages set forth above, and those made apparent from theforegoing description, are efficiently attained. Since certain changesmay be made in the above construction without departing from the scopeof the invention, it is intended that all matters contained in theforegoing description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:
 1. A method of providing voice call, short messageservice (SMS), and data roaming services to a user equipment (UE)subscribed to a Greenfield LTE home public mobile network (HPMN) withoutcircuit switch fallback capabilities and roaming in a 2G/3G visitedpublic mobile network (VPMN), the method comprising: providing anInterworking Function (IWF) in communication with both the HPMN and theVPMN, the IWF having a Proxy Call Session Control Function (P-CSCF), aHome Location Register (HLR), and Short Message Service Center (SMSC)components; receiving a request from the UE to access voice call, SMS,or data roaming services in the VPMN, wherein the VPMN is a 2G/3G mobilenetwork; converting between a Mobile Application Part (MAP) protocol ofthe VPMN and a Diameter protocol of the HPMN to authenticate the UE inthe VPMN; receiving a Packet Switched (PS) Profile for the UE from theHPMN; sending a pre-defined Circuit Switch (CS) Profile to the VPMNinstead of the PS Profile; responsive to the VPMN accepting the CSProfile, establishing a CS Registration between the IWF and the VPMN;establishing a Session Initiation Protocol (SIP) Registration betweenthe IWF and the HPMN; and wherein the steps establishing both the CSRegistration with the VPMN and the SIP Registration with the HPMN enableprovision of the voice call, SMS, and data roaming services to the UEsubscribed to the HPMN while the UE is roaming in the VPMN, wherein HPMNis the Greenfield LTE mobile network without circuit switch fallbackcapabilities and the VPMN is a 2G/3G mobile network.
 2. The method ofclaim 1, wherein to authenticate the UE in the VPMN, the IWF converts aMAP Send Authentication Information (SAI) Message originating from theVPMN to a Diameter S6d interface Authentication Information Request(AIR) Message and transmits the AIR Message to a Home Subscriber Server(HSS) of the HPMN, and the IWF converts an Authentication InformationAnswer (AIA) Message received from the HSS to a MAP SAI Response Messageand sends the MAP SAI Response Message to the VPMN.
 3. The method ofclaim 1, wherein the IWF is hosted on the IP Packet eXchange (IPX)network.
 4. The method of claim 1, wherein registration for dataservices in the VPMN comprises the steps of a Serving General PacketRadio Service (GPRS) Support Node (SGSN) sending a GPRS Location Updatemessage to the IWF, and the IWF returning the PS profile to the SGSN. 5.The method of claim 1, wherein call delivery to the UE comprises thesteps of a Serving Call Session Control Function (S-CSCF) of the HPMNforwarding a SIP Invite message to the P-CSCF component of the IWF; theHLR component of the IWF querying a Visited Location Register (VLR) ofthe VPMN for a Mobile Subscriber Roaming Number (MSRN) of the UE andreturning the MSRN to the P-CSCF component of the IWF; the P-CSCFcomponent of the IWF sending the SIP Invite message to Media Gateway(MG) of the HPMN.
 6. The method of claim 5, wherein for IMS originatingcalls, the MG provides interworking between Integrated Services DigitalNetwork User Part (ISUP) and SIP signaling for call control.
 7. Themethod of claim 1, wherein call delivery for call originating from theUE to an IMS subscriber comprises the steps of a Mobile Switching Center(MSC) of the VPMN sending an ISUP message to a MG of the HPMN; the MGsending a SIP Invite to a S-CSCF of the HPMN; and the S-CSCF routing theSIP Invite to a P-CSCF within the IMS subscriber's home network.
 8. Themethod of claim 1, wherein call delivery for call originating from theUE to a Called Party subscribed to a Public Switched Telephone Network(PSTN) comprises the steps of a MSC of the VPMN sending an ISUP messageto a Gateway Mobile Switching Center (GMSC) of the Called Party's homenetwork; the GMSC requesting a MSRN assigned to the Called Party from aHLR within the Called Party's network, and the GSMC using the MSRN toroute the call to the Called Party.
 9. The method of claim 1, whereinsending of an SMS message originating from the UE comprises the steps ofa MSC of the VPMN routing the SMS message to the IWF; the IWF retrievingthe UE's Mobile Station International Subscriber Directory Number(MSISDN) from the SMS message; the P-CSCF component of the IWF sending aSIP SMS Message to a S-CSCF of the HPMN; and the S-CSCF forwarding theSIP SMS Message to an IP-SMSC within the HPMN.
 10. The method of claim9, wherein an SMSC address provisioned in the UE is that of the IWF. 11.An Interworking Function (IWF) for providing voice, short messageservice (SMS), and data roaming services to a user equipment (UE)subscribed to a Greenfield LTE home public mobile network (HPMN) withoutcircuit switch fallback capabilities and roaming in a 2G/3G visitedpublic mobile network (VPMN), the IWF configured to execute the stepscomprising: converting messages between a Mobile Application Part (MAP)protocol of the VPMN and a Diameter protocol of the HPMN to authenticatethe UE in the VPMN, wherein the VPMN is a 2G/3G mobile network and theHPMN is an LTE mobile network; receiving a Packet Switched (PS) Profilefor the UE from the HPMN; sending to the VPMN a pre-defined CircuitSwitch (CS) Profile instead of the PS Profile returned by the HPMN;responsive to the VPMN accepting the CS Profile, establishing a CSRegistration with the VPMN; and establishing a Session InitiationProtocol (SIP) Registration with the HPMN; wherein by establishing boththe CS Registration with the VPMN and the SIP Registration with theHPMN, the IWF enables provision of the voice, SMS, and data roamingservices to the UE subscribed to the HPMN while the UE is roaming in theVPMN, wherein HPMN is the Greenfield LTE mobile network without circuitswitch fallback capabilities and the VPMN is a 2G/3G mobile network. 12.The IWF of claim 11, wherein to authenticate the UE in the VPMN, the IWFconverts a MAP Send Authentication Information (SAI) Message originatingfrom the VPMN to a Diameter S6d interface Authentication InformationRequest (AIR) Message and transmits the AIR Message to a Home SubscriberServer (HSS) of the HPMN, and the IWF converts an AuthenticationInformation Answer (AIA) Message received from the HSS to a MAP SAIResponse Message and sends the MAP SAI Response Message to the VPMN. 13.The IWF of claim 11, wherein the IWF is hosted on the IP Packet eXchange(IPX) network.
 14. The IWF of claim 11, wherein registration for dataservices in the VPMN comprises the steps of a Serving General PacketRadio Service (GPRS) Support Node (SGSN) sending a GPRS Location Updatemessage to the IWF, and the IWF returning the PS profile to the SGSN.15. The IWF of claim 11, wherein call delivery to the UE comprises thesteps of a Serving Call Session Control Function (S-CSCF) of the HPMNforwarding a SIP Invite message to a Proxy Call Session Control Function(P-CSCF) component of the IWF; a Home Location Register (HLR) componentof the IWF querying a Visited Location Register (VLR) of the VPMN for aMobile Subscriber Roaming Number (MSRN) of the UE and returning the MSRNto the P-CSCF component of the IWF; the P-CSCF component of the IWFsending the SIP Invite message to Media Gateway (MG) of the HPMN. 16.The IWF of claim 15, wherein for IMS originating calls, the MG providesinterworking between Integrated Services Digital Network User Part(ISUP) and SIP signaling for call control.
 17. The IWF of claim 11,wherein call delivery for call originating from the UE to an IMSsubscriber comprises the steps of a Mobile Switching Center (MSC) of theVPMN sending an ISUP message to a MG of the HPMN; the MG sending a SIPInvite to a S-CSCF of the HPMN; and the S-CSCF routing the SIP Invite toa P-CSCF within the IMS subscriber's home network.
 18. The IWF of claim11, wherein call delivery for call originating from the UE to a CalledParty subscribed to a Public Switched Telephone Network (PSTN) comprisesthe steps of a MSC of the VPMN sending an ISUP message to a GatewayMobile Switching Center (GMSC) of the Called Party's home network; theGMSC requesting a MSRN assigned to the Called Party from a HLR withinthe Called Party's network, and the GSMC using the MSRN to route thecall to the Called Party.
 19. The IWF of claim 11, wherein sending of anSMS message originating from the UE comprises the steps of a MSC of theVPMN routing the SMS message to the IWF; the IWF retrieving the UE'sMobile Station International Subscriber Directory Number (MSISDN) fromthe SMS message; a P-CSCF component of the IWF sending a SIP SMS Messageto a S-CSCF of the HPMN; and the S-CSCF forwarding the SIP SMS Messageto an IP-SMSC within the HPMN.
 20. The IWF of claim 19, wherein an SMSCaddress provisioned in the UE is that of the IWF.